1. Field of the Invention
The present invention relates to electric power control of a wireless communication terminal, and more particularly to a control algorithm for compensating a loss due to a temperature variation in a wireless communication terminal.
2. Description of the Related Art
In general, a wireless communication terminal is designed to control its transmitting power depending on a variation in a distance between the wireless communication terminal and a base station. As the wireless communication terminal is moved away from the base station, the required amount of sending power of the wireless communication terminal increases, whereas as the wireless communication terminal is moved near to the base station, the required amount of sending power of the wireless communication terminal decreases. Practically, the sending power of the wireless communication terminal is controlled in such a fashion that it is inversely proportional to a received signal strength indicator (RSSI) measured in the wireless communication terminal.
For example, in a case where both a wireless communication terminal A located apart from a base station by 100 m and another wireless communication terminal B located apart from the base station by 1 km send simultaneously a signal to the base station at a same power level, respectively, since the terminal B is 10 times as remote as the terminal A from the base station, there is 10.sup.3.about.10.sup.5 difference in power received at the base station from terminal A and terminal B. In this case, the base station cannot restore the signal received from terminal B. As mentioned above, when two terminals A and B located apart from the base station by a distance different from each other send simultaneously signals to the base station at a same power level, respectively, there has been a problem in that, it is impossible for the base station to restore the received signal of the terminal B relatively remote from the base station. The problem is called "a near-far interference problem". When a sending/received power level is very low, a bit error rate becomes high, whereas when the sending/received power level is very high, another terminal (especially a remote terminal, such as terminal B) receives great interference, which results in a deterioration of system performance. Accordingly, appropriate regulation of sending output of a wireless communication terminal should allow a signal received by the base station to generate the minimum power ratio of signal to interference. This power control enables reduction of power consumption of a wireless communication terminal and increases subscriber capacity.
As shown in FIG. 3, a wireless communication terminal controls electric power using a code. However, the ratio of input to output of an amplifier are as shown in FIG. 1a. The ideal ratio of input to output of the amplifier represents a linear characteristic as shown in FIG. 1b. But, the input/output characteristic of an actually implemented amplifier is indicated by a nonlinear form or an exponential form as shown in FIG. 1A and depends on factors such as constituent circuits of the wireless communication terminal, a temperature of the wireless communication terminal, and a frequency band in use.
Particularly, an output characteristic of the amplifier can be changed depending on a temperature variation as shown in FIGS. 2A and 2B. There has been a problem in that, for a signal having a high decibel (dB), as a temperature increases, an output value increases, whereas for a signal having a low decibel (dB), as a temperature increases, an output value decreases. See FIG. 2a. Accordingly, storage of output values depending on a temperature variation for each signal allows electric power to be controlled as shown in FIG. 2b. But, in this case, a problem arises in that, the capacity of a memory in use grows. Consequently, conventionally, a temperature table which records output value of each signal depending on a high temperature, the normal temperature, and a low temperature had been stored, and then electric power for output has been determined on the basis of the stored temperature table. However, consideration of only three options makes it impossible to precisely control the output electric power.